Covering foe



D. FINLEY Aplrfi 23, 1935.

COVERING FOR CURING CONCRETE Filed June 1, 1951 INVENTOR 22/5? F/IVZ. E)

///.5' ATTORNEY Patented Apr. 23, 1935 .ITED STATES PATENT OFFICE 9Parafline Companies, Inc.,

San Francisco,

Calif, a corporation of Delaware Application June 1,1931, Serial No.54111,,M6

4 Claims.

My invention relates to a covering to be used on concrete during thecuring or drying state to preserve the desired moisture content.

It is among the objects of my invention to 5 provide a covering thatwill maintain a body of concrete in a moist state during the drying orcuring process and supply Water in addition to that in the original mixwhere it is desirable or necessary.

Another object of the invention is the provisio of a covering that is inconvenient form for use, and that is capable of repeated use.

A further object of the invention is to provide a covering that willimprove the surface quality of concrete by preventing chilling of thesurface by evaporation of moisture therefrom.

Referring to the drawing:

Figure 1 is a section taken through the covering material of myinvention, illustrating in section a portion of a wet'concrete slab overwhich the covering is laid.

Figure 2 is a view similar to Figure 1, but showing a variantconstruction which is particularly applicable to floor slabs ofbuildings; and

Figure 3 is a similar view, on reduced scale, showing another variantform of construction.

In terms of broad inclusion, the covering for curing concrete embodyingmy invention comprises an integrally formed sheet having a waterabsorbent base layer over which is secured a layer of materialimpervious to the passage of moisture. This covering sheet is laid onthe finished concrete surface in a moist or wet condition; it being heldin place by any suitable means, so that the edges of the covering aresealed to prevent the escape of moisture. The covering prevents anymaterial evaporation of moisture from the concrete and the moist base,supplies additional water needed for curing, and thus developspractically the ultimate strength obtainable by complete water curing.Preferably the covering sheet is raised slightly above the surface ofthe concrete, so that a water space is provided for excess water to poolunder the absorbent base layer.

In the preferred form of my invention the water absorbent base layercomprises a fibrous sheet, such as rag "felt, and the moistureimpervious layer comprises a coating of a cold cementing compound, suchas paint. The use of a cold cementing compound in the waterproof layeris highly desirable, because it may be applied by simple operations,such as by brushing or spraying and without the requirement that heat beused. In this .way the preparing of the curing material for use, or itsmanufacture, avoids the use of special machinery of complicated natureinvolving heated machine elements, supply tanks for holding the moltenproduct, and the like which are necessary in the application of hotcementing compounds, such as bitumen.

For use in buildings, or in other locations where workmen are movingabout, the covering employed is preferably one embodying a protectivesurface layer comprising a tough and preferably waterproof membrane-sucha membrane as to kraft paper, or a metallic membrane of metal foil, forinstance. This tough surface permits light tramc over the covering whenlaid in place, and therefore does not interrupt the operations of otherworkmen. The top surface membrane 15 also aids in the cure of theconcrete by assisting the paint layer in the retention of the addedwater held by the absorbent base. When made of a waterproof material thetop surface membrane may conveniently alone serve as the moisture 20impervious layer. In this case the membrane may be secured over the basesheet by stitching,

' stapling, or other means providing a mechanical tie.

The color of the top surface of the covering 5 may also assistmaterially in controlling curing temperatures. If the covering is to beused in a comparatively cool climate it may be desirable to use a blackcolored top surface to absorb the maximum amount of heat; or, if it isto be used in an excessively hot climate, the top surface may besuitably colored to reflect heat and thus keep the concrete at a lowertemperature than would otherwise obtain. As the ultimate strength is afunction of curing temperature it is thus possible to improve thejquality of concrete in areas of climatic extremes. It is to be notedfurther that, by preventing evaporation from the surface of theconcrete, the covering prevents localized chilling of the surface byevaporation of moisture therefrom, which is a frequent cause of surfacecracking.

In terms of greater detail, and referring particularly to Figure 1, thecovering for curing concreteJembodying my invention comprises a waterabsorbent layer 2 preferably. a sheet of fibrous material, such as a ragfelt having a weightv preferably of between 15 to '75 pounds per 480 sq.ft. It is to be noted however that other ma terials may be employed inthe water absorbent layer 2; the important thing being, of course, thatthe material exhibits water-holding properties.

A moisture impervious layer 3 of a cold cementing compound is coated onthe upperv side of the sheet 2. unitary covering is thenlaid, preferablyin a wet condition on a concrete slab 4 to preserve the moisture contentduring the curing period.

There are several cold cementing compounds that can be used in thewaterproofing layer 3, but I have found a very satisfactory coating canbe obtained by applying paint. The paint prefer.- ably used is onehaving decided cementitious characteristics, and, at the same time,highly moisture impervious qualities. Such a paint may 'be made byraising three hundred pounds of rosin to 450 F., and adding theretotwenty-one pounds of flaked sodium hydroxide (anhydrous) the mixturebeing held at 475 F. until the sodium hydroxide is all taken up. Eightygallons of drying oil, either linseed oil, perilla oil, China-wood oil,or mixtures of one or more of these with sardine oil or soya bean oil,are then added; the drying oil being added gradually and the temperatureraised to about 500 F. while the first portions are being added, andgradually allowed to drop to 400 F. as the final amounts are added.

Four pounds of red lead are then cooked in at 400 F., after which themixture is withdrawn from the fire and ten gallons additional of thedrying oil are added along with three pounds of manganese resinate.Finally, at about 225 F., one hundred and thirty-five gallons of waterare added, and, when the mixture has cooled, thirtyfour hundred poundsof slate or shale dust, or equivalent filler of approximately the samespecific gravity, are also added- This paint may be spread by brushes,scrapers or may, after further thinning with water, be applied byspraying. By using acold cementing compound, such as the paint abovedescribed, in the layer 3 the same maybe applied by simple operations,and without the requirement that heat be used. In this way themanufacture of the curing material is greatly facilitated.

While the above mentioned paint has been set forth as being preferablyused in the waterproof ing layer 3, it has been found that other coldcementing compounds may be used. Soluble silicates may be employed,particularly as it is found that these tend to become insoluble afterdrying and standing for a considerable time. Rubber latex may also beused, as it is both cementitious and moisture impervious. Resin, bothnatural and artificial, when out back with softening oil to lessen itsbrittleness, may also be used in the waterproofing layer.

Preferably a second coat 5, one employing linseed oil, a varnish and apigment, is applied over the paint last described. I have found that asatisfactory paint in the top coat 5 may be made by mixing togetherthree and one-half pounds of raw linseed oil, seven pounds of groundshale or slate, two pounds of vamish and one pound of turpentine. To theabove, dryer in suitable amounts may be added as required.

For use in buildings, or in other locations where workmen are movingabout, it is highly desirable that the covering be such that persons maytread over its surface. Figure 2 shows a variant form of structure tomeet with these conditions, in which a tough and preferably a waterproofmembrane 6 is provided as a surface sheet over the layer 3. This toughsheet not only permits light traffic over the covering when laid, butalso aids in the cure of the concrete by assisting the paint layer 3 inthe retention of the added water held by the absorbent sheet 2. i

A tough fibrous sheet, such as kraft paper, is preferably used in thisconnection and is preferably embedded in the coating 3 of paint whilethe same lies still wet on the surface 'of the absorbent layer 2. Thetwo sheets 6 and 2 are then pressed gently together by rolls, and'intheir united form are passed into suitable drying racks. Finally thecomposite covering sheet is rolled up on winding machines and suitablypacked in the rolled form for marketing.

A suitable kraft paper for this surface sheet may be one weighing thirtypounds per 2,880 sq. ft. It is obvious that heavier sheets may be usedin the membrane 6 where greater resistance to traific is desirable,while lighter sheets may be used where the somewhat diminished strengthof such lighter sheets does not detract from theutility of the finishedproduct. In other words, the weight and strength of this surface sheetare proportioned to the service to be encountered, and

determined also by the cost of the finished material. Sulifite, straw,jute and other similar materials maybe used in thesheet 6. Anyof thesemay be made partially or highly waterproof by waxing, oiling or thelike. A suitable treatment is to saturate the top sheet with China-woodoil, as this oil is highly resistant to the transmission of water ormoisture thru its films. Linseed oil, vegetable waxes, fatty oils,resins, fats, waxes, and/or resins may also be used to treat the surfacemembrane, and may be used either as a saturant or as a coating, or both.

While the surface sheet 6 is preferably united to the absorbent layer 2by means of the cemenas by means set forth in the above paragraph;

As a further alternate in construction, a flexible metal, such as themetal foils, may be used as the surface or traflic sheet. Figure 3 showsa metallic sheet 1 overlying and stapled to the absorbent sheet 2. Themetallic surface sheet may also be applied to the layer 2 as a coating,such as by spraying or by electro-depositing.

In applying the material over a concrete slab 4, the covering sheets arepreferably unrolled from suitable spindles inserted to the hollow coresof the rolls, and are wetted as they are laid over the concrete; theconcrete having reached and passed a state of initial set at this time.Additional water is preferably flooded under the covering until thelatter almost floats. It may be desirable to hold the covering sheetaway from the surface of the concrete slab, so that a water space isprovided. This may be accomplished by any suitable means, such as by athin sprinkling of coarse sand. The spacing is preferably such as 7 toraise the water absorbent layer 2 up about an eighth of an inch abovethe surface of the concrete. Note Figure 3, in which the covering sheetis raised slightly off the concrete surface. When water is flooded underthe covering that which is unabsorbed by the layer 2 will pool in thespace provided. As the pooled water is fed to the concrete the former isreplenished by the store in the felt. Thus a thinner felt, holding alesser volume or weight of water, may be made to serve in place of a.thicker felt laid directly on the concrete. I

The advantage of this method over open pondingis, of course, that thepended water is autothe boundary of the covering are preferably weighteddown by piles of dirt, or'other suitable means, so thatthe entirecovering sheet is sealed down over the concrete to prevent the escape ofmoisture. When the cure is deemed to have been effected, in the ordinarycase and with the ordinary Portland cement concrete, this will be inabout ten days, the curing material is removed. The covering may be usedrepeatedly as its construction is such that good durability is attachedtoit.

n steeply inclined concrete surfaces, practically the same procedureapplies except thatrthe covering may have to be secured against slidingdown. On vertical walls and the like it is obvious that the coveringwould have to be suspended or otherwise supported in contact with theconcrete mate strength of concrete is closely dependent on its moisturecontent at the various stages of cure, and in part on the temperatureduring curing, and modern specifications are frequently as muchconcerned with moisture content and method of curing as they are withother ratios and qualities.

To secure the highest strength and most economical combination ofmaterials, and to obtain the complete hydration of the cement it hasbeen the practice to keep the newly laid concrete in a wet condition bysprinkling or open ponding to insure a proper cure. In arid regions thelarge amounts of water needed for sprinkling or open ponding may beexpensive, or not available, and on inclined or vertical surfacessprinkling or ponding treatment is dimcult if not impossible because thewater flows away by gravity. Accordingly various attempts have been madeto effect a cure of concrete by means other than those requiring excessamounts of water. i

A moisture impervious covering alone has been tried, but, without meansfor holding additional moisture, it does not operate satisfactorily,because the moisture evaporated from the surface of the concretecondenses on the surface of the impervious covering and flows down alongthe unavoidable wrinkles and away from the areas where it is needed.Furthermore, such a covering when merely laid over the concrete permitssome circulation of air beneath it, which circulation operatesconstantly to reduce the moisture content at the surface of the concretebeing cured. Such a covering can not supply additional water needed forhydration.

Furthermore, merely placing a second layer of moisture absorbentmaterial beneath the moisture impervious layer does little to correctthese defects, since the dense top covering cannot be held insufliciently intimate contact with the moisture absorbent layer toprevent circulation of air and subsequent loss of moisture.

Such separate coverings are also more expensive to apply than my unitarycovering, because of the extra time. required to lay two coverings, and.becausev of the further expense involved since such coverings are soweak mechanically that they can ordinarily be used but once. In thecovering of my invention the water stored in the material contributes tothe complete hydration of the cement, and the improved mechanicalstrength of the unitary structure permits repeated use. When used onhighways the material can be wetted and laid in one operation, by amachine if desired, and a practically perfect cure obtained. Even wherewater is so plentiful that ponding or sprinkling might be employed, thecovering of my invention produces a concreteof improved and more uniformstrength because of the closely controlled temperature and moistureconditions, and at a saving in expense.

As a rule highways are defective largely because of the improper curing,particularly at thev surface which spalls off under traflic. The use ofthe covering of my invention will prevent a repetition of such waste,since actual tests under the severest of conditions have demonstratedthat when cured under my covering a concrete road slab will developpractically its full standard water cured strength. This means that athinner slab can be used, and still developed as much strength as'thosepreviously employed, and also will present a superior traffic surface.

These remarks apply with equal force when the curing material of myinvention is used on irrigation ditches and the floor slabs ofbuildings.

In the latter case the effect is multiplied since,

by lightening the floor slabs in the upper stories,

the entire frame structure down to and including the foundation can alsobe lightened propor: tionately. It is thus feasible to save as much asof the cost of ooncretematerials used in a tall building.

In conclusion, and looking at the problem from a different angle, it ispointed out that the ultimate strength of concrete cannot be obtained byendeavoring to provide suflicient water to the mix when it is poured.When a wet mix is poured a large amount of cement is actually carriedaway and lost as the water runs out of the forms, and when the mixfinally sets the pores that are left by the final evaporation of theexcess water operate to materially weaken the concrete. In order to makeup for this weakening the tendency is to add more cement. This resultsnot only in a greater cost, but also in a more pronounced expansion andcontraction with changing moisture content. This latter is highlyundesirable in slabs which are not permitted free movement, such as roadslabs, bridge slabs positioned between structural steel members, andstucco coats. Actually,

\the ultimate strength in concrete is obtained by use ofsmallproportions of cement, and in a mix which is poured in a fairly drystate. This means however that sufficient water for the completehydration of the cement is not present in the mix, and that additionalwater must be fedto the slab during the curing. By use of the coveringembodying my invention the ideal mix may be used, because not only isthe original water used in the mix retained, but also means are provlded for supplying additional water if such is needed for completehydration.

I claim:

1. The method of curing concrete which comprises overlaying the surfaceof the concrete with a moisture retaining material, holding the materialabove said surface, and flooding the space between the material andsurface with water.

ing the space between the sheets and surface with water.

4. The method of curing concrete which comprises overlaying the surfaceof the concrete with a water absorbent sheet, apply water to saturatethe sheet, and then flooding additional water over the surface of theconcrete'until the sheet substantially floats.

DOZIER FINLEY.

